arf.rb

class ARF
    attr :coords
    def initialize map, follow, size, app
        @map, @follow, @size, @app, @coords = (map.is_a?(Array) ? map : [map]), follow, size, app, [follow.left,follow.top]
        @vx, @vy = 0,0 # velocity
        animate_loop
    end
    def [](x,y)
        @coords[0] += x
        @coords[1] += y
        @follow.move *@coords
        @coords
    end
    def animate_loop
        map, follow, size = @map, @follow, @size
        sc = method :[]
        gc = method :coords
        si = method :instance_variable_set
        gi = method :instance_variable_get
        @app.instance_eval do
            animate 12 do
                si['@vx',gi['@vx']-1] if gc[][0] > size[0]*0.7
                si['@vx',gi['@vx']+1] if gc[][0] < size[0]*0.3
                si['@vy',gi['@vy']-1] if gc[][1] > size[1]*0.7
                si['@vy',gi['@vy']+1] if gc[][1] < size[1]*0.3
            end
            animate do
                map.each {|o| o.move(o.left+gi['@vx'],o.top+gi['@vy']) }
                sc[gi['@vx'],gi['@vy']]
            end
            animate 6 do
                si['@vx',gi['@vx']-(gi['@vx']<=>0)]
                si['@vy',gi['@vy']-(gi['@vy']<=>0)]
            end
        end
    end
end

example.rb

require 'camera'
Shoes.app(:width=>320,:height=>240) {
    @co = ARF.new(image(1024,768){fill red..blue, :angle => 45; rect 0,0,1023,767},image(24,24){fill lime; rect 0,0,23,23},[320,240],self)
    animate do
        b,x,y = self.mouse
        next unless b == 1
        @co[-5,0] if x < 320*0.7
        @co[+5,0] if x > 320*0.3
        @co[0,-5] if y < 240*0.7
        @co[0,+5] if y > 240*0.3
    end
}